Centrifugal pump having hydraulic seal means



June 2, 1970 3,515,497 CENTRIFUGAL PUMP HAVING HYDRAULIC SEALMEAN5 Filed Aug. 27, 1968 E J. a. STUDEBAKER. ET AL 4 Sheets-Sheet 1 INVENTORS. JAMES B. STUDEBAKER IRV/N F ZAGAR LAWRENCE 7. GOBBLE ATTORNEYS June 2, 1970 J. B. STUDEBAKER ET AL 3,515,497

CENTRIFUGAL PUMP HAVING HYDRAULIC SEAL MEANS Filed Aug. 27, 1968 4'Sheets-Sheet 2 INVENTORS JAMES B. STUDEBAKER IRVIN F ZAGAR LAWRENCE T GOBBLE A ZZMMZMLJ Mai- 2275 A ATTORNEYS June 1970 J. B. STUDEBAKER ET AL' 3, 1 7

7 CENTRIFUGAL PUMP HAVING HYDRAULIC SEAL MEANS Filed Aug. 27, 1968 4 Sheets-Sheet 3 INVENTORS. JAMES B. STUDEBAKER /RV/N F ZAGAR LAWRENCE 7. GOBBLE ATTORNEYS CENTRIFUGAL PUMP HAVING HYDRAULIC SEAL MEANS Filed Aug. 27, 1968 June 2, 1970 J. asTUDEBAKER 4 Sheetsfiheet 4 ATTORNEYS I'INVE'NTORS B. STUDEBAKER IRVIN F Z AGAR JAMES LAWRENCE 7." GOBBLE United States Patent US. Cl. 415-112 8 Claims ABSTRACT OF THE DISCLOSURE Hydraulic seal producing expeller means is provided between the impeller of the pump and sealing means which seals 9. valvular space between the pump shaft and the adjacent casing. The expeller means includes a plurality of separate axially spaced expeller plates carried by the shaft and having vanes thereon. The plates are separated from one another by separator plate means carried by the casing. Purging means includes an arrangement for introducing fluid under pressure into the expeller means. Means is also provided for introducing fluid into the space between oppositely pumping expeller plates to provide a vapor seal.

BACKGROUND OF THE INVENTION The present invention relates to centrifugal pumps commonly termed sand or slurry pumps which are adapted to pump corrosive liquids or liquids carrying grit, sand or other insoluble particles therein. This type of centrifugal pump is so constructed as to avoid the necessity of employing a stufiing box or gland between the impeller shaft and the pump casing.

In such centrifugal pumps, an annular valvular space is provided between the pump shaft and the associated pump casing whereby a non-friction arrangement is provided when the pump is running. A valve member of annular construction is provided for normally closing the valvular space, this valve member being automatically operated to open the valvular space when the pump is running, the valve member automatically serving to close off this valvular space when the impeller shaft stops rotating.

In order to prevent leakage of pumped fluid from the pump through this valvular space, means is provided for forming a hydraulic sealing pressure, this means comprising suitable pump expeller components.

The present invention represents an improvement over U.S. Pat. No. 2,660,487 wherein a valve means similar to the present invention is provided in the same general combination including a centrifugal pump having expeller means for providing a hydraulic seal.

Prior art arrangements such as shown in the aforementioned patent are limited in that the expeller means thereof will accommodate only a limited amount of internal pump fluid pressure without experiencing leakage. It has been found desirable to employ internal pump fluid pressures greater than those which can be effectively maintained without leakage with known arrangements.

A further problem arising in the use of known pumps of this type is the fact that there is no means provided for purging the expeller means. This is an important consideration in those cases where the fluid that is being pumped solidifies, hardens or cakes when the pump is not operating such as in the case of cements. In these instances, it is important to provide a means for purging such material from the multiple cavities of the expeller means.

Known constructions of similar pumps do not provide a means for forming a liquid barrier or vapor seal in the 3,515,497 Patented June 2, 1970 ice expeller means. Consequently, there is no means for preventing air leakage into the pump or for preventing external leakage of fumes or vapors arising from the liquid being pumped. Additionally, such pump ararngements cannot operate with a negative suction head since air can freely enter the pump when the expeller means are not sealing the pumped fluid.

SUMMARY OF THE INVENTION In the present invention, the expeller means includes a plurality of expeller plates having vanes formed thereon. The present invention employs a main expeller as in the prior art and in addition, provides one or more secondary expeller plates which may be of any diameter. Since the effectiveness of the expeller action is dependent upon rotation speed, the outer diameter size of the expeller and the magnitude of the clearance which is maintained with adjacent stationary plates, the amount of internal pump pressure that can be counteracted by the expeller means at any pump speed can be increased by two if one auxiliary expeller plate is employed along with the main expeller.

In a similar manner, the internal pump pressure that can be accommodated may be increased by three times if two additional expeller plates are utilized, and the number of expeller plates may be increased to provide the desired degree of hydraulic sealing pressure provided by the expeller means.

The expeller plates of the present invention may be of substantially identical construction so as to be readily interchangeable and to be of simple and inexpensive construction. In a similar manner, the separator plate means of the present invention may all be substantially identical with one another.

The present invention incorporates purging means by providing internal drilled passages in certain of the components of the apparatus whereby external plumbing connections may be interconnected with the apparatus and clear water may be introduced into the expeller means.

The drilled passages may open through a wall of the outermost portion of the expeller means whereby clean water may be introduced at this portion of the expeller means so as to flow back toward the main expeller and the impeller of the pump to flush out the cavities between the various portions of the expeller means so that this portion of the structure is effectively purged.

In a modified form of the invention, certain expeller plates are so arranged that the vanes thereof are adapted to pump liquid in opposition to one another. Means is additionally provided for introducing a clean neutral fluid from external plumbing into the space between these latter mentioned plates. Pressure which is then applied from either direction into the space between such plates forces a liquid leg into the pumping expeller vanes on the low pressure side thereby creating a centrifugal pressure force opposing the applied pressure. Accordingly, a liquid barrier is provided that effectively prevents passage out of the pump of fluid vapors and passage into the pump of air thereby forming a vapor seal. In this manner, the slurry pump may operate with a negative suction head.

A close axial clearance is maintained 'betwen the outer face of the main expeller and adjacent stationary plate to limit the size of slurry or sand particles that may pass through this clearance. This tends to reduce the rate of wear and abrasion between expeller sealing components.

The expeller means of the present invention includes longitudinally spaced expeller plates secured for rotation with the pump shaft and stationary separator plate means between the expeller plates and secured to the casing. The expeller plates have vanes thereon for pr ducing the desired pumping action. Close axial clearance is maintained between the vanes and the adjacent stationary separator plate means to minimize cross-vane leakage and improve the eifective sealing efficiency of these components. As is the case with the main expeller, the auxiliary expeller plates rotate with the pump shaft and spin any liquid or slurry located in the expeller cavity formed between the expeller plates and the separator plate means, producing centrifugal forces on the fluid that create a differential pressure increasing radially outwardly thereby tending to oppose internal pump pressures and minimizing or preventing the outflow or leakage of liquid along the pump shaft.

A larger clearance is maintained on the side of the expeller plates not having the vanes thereon and the adjacent stationary portions or separator plate means to allow any slurry particles to move or freely rotate without undue rubbing or abrasion to thereby reduce wear or scuffing.

The expeller plates as well as the separator plate means are mounted so as to be readily removable, the expeller plates being keyed to the pump shaft. In order to ensure positive positioning of the expeller plates in operative position, a sleeve is disposed around the shaft for urging the expeller plates into proper operative position. An annular resilient member such as a rubber ring is positioned between the main expeller and this sleeve and provides an axial biasing force to ensure proper p sitioning of the expeller plates. This rubber ring or similar means is compressed when the components are assembled into operative relationship. The principal advantage of this construction is that it does not require extremely close dimensional tolerances that would otherwise be required. It also simplifies assembly of the components by eliminating complicated and costly positioning and clamping arrangements such as snap rings 01' bearing nuts and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view partly broken away of a centrifugal pump according to the present invention;

FIG. 2 is an enlarged longitudinal sectional view of a portion of the structure shown in FIG. 1;

FIG. 3 is a sectional view taken substantially along line 3-3 of FIG. 2 looking in the direction of the arrows;

FIG. 4 is a sectional view taken substantially along line 44 of FIG. 2 looking in the direction of the arrows;

FIG. 5 is a sectional view taken substantially along line 55 of FIG. 2 looking in the direction of the arrows;

FIG. 6 is a sectional view taken substantially along line 66 of FIG. 2 looking in the direction of the arrows;

FIG. 7 is a longitudinal sectional view of a portion of a pump structure similar to that shown in FIG. 2 and illustrating a modified form of the invention; and

FIG. 8 is a longitudinal sectional view of a further modification of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings wherein like reference characters designate corresponding parts throughout the several views, as seen in FIG. 1, a slurry pump includes a base member 10 including a horizontal base portion 12. A rear upright portion 14 extends upwardly from base member 10, and a forward support portion 16 is provided on the base member. A member 18 is rigidly afiixed to portion 16 of the base member, and the intake portion 20 of the casing of the pump is formed integral therewith. An intermediate annular casing portion 22 is disposed adjacent the intake portion 20, an annular sealing member 21 being disposed therebetween and formed of rubber or the like. A discharge casing portion 24 is supported adjacent portion 22, and has a discharge 4 neck 26, the intake neck for the intake portion of the casing not being shown in the drawings.

A conventional impeller shaft 30 is rotatable on two separate bearings which are supported in cylinder 36 which in turn is supported at the outer end by the pedestal 14 and pedestal cap 32. The inner end terminates at the attaching flange 38. The inner bearing is disposed within the portion indicated by reference numeral 34 of cylinder 36.

As seen most clearly in FIG. 2, flange 38 is secured by a plurality of bolts 40 with a cage 42 defining a longitudinally extending cylindrical portion as hereinafter more fully described. This cage has an opening 46 for venting the pump to atmosphere.

A generally L-shaped gland ring 50 is supported by a plurality of studs 52 secured to the intake portion 20 of the casing, these studs extending through suitable holes provided in the gland ring and having nuts 54 threaded on the outer threaded ends thereof. The gland ring is adapted to compress an annular sealing member 56 such as a rubber ring in the operative position illustrated so as to provide an effective seal with the die-ring hereinafter described.

A conventional impeller 60 is secured to the forward end of the pump shaft 30 and removably mounted thereon by a nut '62 threaded on an outer threaded end of the shaft. This construction enables the components of the expeller means to be readily assembled and disassembled as hereinafter pointed out.

The main expeller 64 includes a portion engaging an angular shoulder 66 of the shaft for properly positioning the main expeller, an annular rubber sealing ring 65 or the like being provided between the impeller and the main expeller to provide a seal therebetween.

As seen in FIG. 4, the main expeller 64 includes a pair of longitudinally extending portions 67 which fit in complementary grooves provided in the inner surface of the hub 61 of the impeller 60 whereby the main expeller rotates with the impeller and the impeller shaft during operation of the pump.

The main expeller includes a smooth contoured surface 68 forming the inlet contour of the intake portion of the casing for directing liquid or slurry into the eye of the impeller. The expeller also defines a plurality of radially directed vanes 70 as seen most clearly in FIG. 3, the outer edges or outer face of this main expeller as indicated by reference numeral 72 running in close proximity 'to an adjacent stationary plate, the close axial clearance limiting the size of slurry or sand particles that may pass through the clearance portion indicated by reference numeral 74. The expeller vanes 70 impart radial centrifugal force to any liquid or slurry positioned between the vanes thereby minimizing or preventing leakage flow radially inwardly from the pump toward the pump shaft.

A basic sleeve surrounds the impeller shaft and row tates therewith, this sleeve having formed at its outer end a cup-shaped labyrinth portion 82 surrounding a stationary cylindrical labyrinth portion 84 having an outer flanged portion 86 fastened by cap screws 88 to the aforementioned flange 38. Suitable annular sealing means 90 are provided within this stationary labyrinth portion 84, the coacting labyrinth portions 82 and 84 constituting a protective device for the adjacent inner bearing means.

This basic sleeve 80 may be of a construction substantially identical to that shown in US. Pat. No. 2,660,- 487 and identical by reference numeral 39 in such patent. Accordingly, no detailed description of the basic sleeve is considered necessary in the present application.

A plurality of weighted levers are pivotally supported by a spider means indicated by reference numeral 102, these levers and spider means being substantially the same as that shown in the aforementioned US. patent. These weighted levers are adapted to act upon a backing plate 104 of similar construction to the backing plate 70 of the aforementioned US. patent, and a valve member 108 is secured to and carried by this backing plate, valve member 108 being similar to the valve member 72 of said aforementioned U.S. patent. The backing plate 104 is normally urged to the left as seen in FIG. 2 by a plurality of spaced springs 110 disposed within suitable cavities 112 of the basic sleeve 80.

The intercooperation of the backing plate, valve member and weighted levers is identical with that discussed in connection with the aforementioned US. patent; and accordingly, no detailed description of the operation thereof is considered necessary.

The expeller means of the present invention includes a pair of auxiliary expeller plates 120 and 124 having integral annular hub portions 122 and 126 respectively. While these auxiliary expeller plates have been shown as two in number, it is apparent that one or more of these expeller plates may be positioned longitudinally along the pump shaft from the main expeller in order to enhance the hydraulic sealing efiect as discussed hereinbefore. It will be noted that the outer diameter of the expeller plates may be substantially the same as that of the main expeller or larger to provide additional leakage resistance. The expeller plates 120 and 124 have radially ex-v tending vanes 130 and 132 formed thereon respectively, and as seen most clearly in FIG. 5, six radially extending vanes 132 are provided on expeller plate 124. It should be understood that any suitable number of vanes may be provided on each expeller plate, and that the expeller plates are of substantially identical construc tion.

As seen most clearly in FIG. 2, the expeller plates 120 and 124 are illustrated in operative position, and movement thereof to the right of the position illustrated is prevented by interengagement of expeller plate 120 with the basic sleeve 80. The expeller plate 120 and 124 are separate from one another and are adapted to be removed from the impeller shaft. The expeller plates are connected for rotation with the impeller shaft by a key 138 fitting within suitable aligned grooves provided in the shaft and the expeller plates.

An annular shaft sleeve 140 is disposed in surrounding relationship to the impeller shaft and is slidable therealong. An annular resilient means 142 in the form of a rubber ring or the like is interposed and compressed between the shaft sleeve and the main expeller so as to normally urge the shaft sleeve to the right as seen in the drawings thereby ensuring positive positioning of the expeller plates 120 and 124 in the operative position illus trated.

An annular die-ring 150 is removably positioned within the intake portion of the casing, the die-ring being smoothly curved on the forward or inward side thereof to minimize fluid passage resistance at the inlet of the pump and to be less subject to abrasion wear from slurry particles passing by the die-ring into the impeller.

A plurality of studs 152, which may be four in number, are permanently attached to the die-ring and extend outwardly through suitable holes provided in the cylindrical portion 44 of the cage previously described. Nuts 154 are threaded on the outer threaded ends of studs 152 to form a clamping arrangement for the separator plates hereinafter described.

A first pair of annular separator plate means 160 and 162 are provided, these plate means as seen most clearly in FIG. 2 being of generally L-shaped cross section. A third stationary or separator plate means 164 is of generally disc-like configuration and may be termed a wash plate. It will be seen in FIG. 2 that these plate means are retained in operative clamped relationship by the intercooperation between the cylindrical portion 44 of the cage and the die-ring 150 so that these plate means are held in stationary position relative to the associated casing.

Suitable packing means 166, 168 and 170 in the form of rubber O-rings or the like are positioned between the outer portions of these plate means and surrounding components to prevent external leakage thereby. A further gasket member 172 is compressed between the plate means 164 and portion 44 of the cage.

The clamping arrangement provided by the die-ring is such that the die-ring can be readily removed thereby enabling the expeller plates and separator plate means to be removed from the pump assembly by sliding the expeller plates off of the impeller shaft toward the impeller end of the shaft, while alternately removing the separator plate means through the openings in the intake portion of the casing. This assembly of the components can be carried out without disturbing the main bearing assembly, shaft or the drive coupling, thereby facilitating maintenance and overhaul.

As mentioned previously, close axial clearance is maintained between the vane side of each of the expeller plates and the adjacent stationary or separator plate. On the other hand, a greater clearance is maintained on the side of the expeller plates not having vanes thereon, and the adjacent stationary plate.

The outward-most stationary plate, or wash plate 164 in this form of the invention performs a three-fold purpose. Firstly, it forms a stationary surface against which the right-hand-most expeller plate 120 coacts in producing the pressure dilferential forces to prevent external leakage. Secondly, it provides a flat rigid surface upon which the flexible diaphragm sealing member 108 of the check valve means seats when the pump is not running to form a positive external seal.

Thirdly, stationary plate means 164 contains internal drilled passages connected to external plumbing so that clear water may be introduced into the outermost expeller cavity to provide a purging action as aforedescribed.

Referring now to FIG. 6, the arrangement for introducing fluid under pressure into the expeller means for carrying out the purging operation is illustrated. A suitable pipe tap is provided on the outwardly facing surface of the cylindrical portion 44 of the cage, and is adapted to be connected with any suitable external source of fluid under pressure. The pipe tap is connected with a longitudinally extending drilled hole which is in communication with a radially extending cross passage 182 which carries the flush fluid to the inner bore of the cylindrical portion 44.

The radially outer face of stationary plate means 164 is provided with an annular groove 186 therein which is so positioned as to receive fluid from the cross passage 182. A radially extending drilled passage 190 is provided in plate means 164, and is in communication with the annular groove 186. Passage 190 in turn is in communication with a drilled passage 192 which extends 1ongitudinally of the pump and opens at the face of plate means 164 which faces the impeller end of the pump.

Accordingly, clean fluid may be introduced through the drilled passages to flow from the outer end of the expeller means toward the main expeller and the impeller of the pump to flush out the expeller cavities when desired. The flow of fluid through the purging means may be controlled by any suitable means such as a valve or the like (not shown).

Referring now to FIG. 7 of the drawings, a modified form of the invention is illustrated wherein parts similar to those previously described have been given the same reference numerals primed. The over-all arrangement is generally similar to that shown in FIG. 2 with the exception that the expeller plate 124' has been modified so that the vanes 132' are on the opposite side of the plate from that illustrated in FIG. 2. Accordingly, the two expeller plates 120 and 124 tend to pump liquid in the direction as indicated by the arrows so that the two expeller plates are pumping in opposition to one another.

In this form of the invention, the means for introducing fluid from an external source of fluid includes a pipe tap 200 corresponding to the pipe tap 180 previously described which is in communication with a longitudinally extending drilled passage 202. This passage in turn is in communication with a cross passage 204 corresponding to the passage 182 previously described. The principal difference in this form of the invention is the fact that the cross passage 204 is disposed at a different longitudinal position along the shaft from the cross pas sage 182. The cross passage 182 is in communication with a drilled passage in the plate means 164, while the cross passage 204 as shown in FIG. 7 is in communication with a drilled passage in the stationary plate means 162'.-

As seen in FIG. 7, cross passage 204 is in communication with an annular groove 206 provided in the radially outwardly facing surface of the stationary plate means 162.

Plate means 162' is in turn provided with one or more radially extending drilled passages 208 in communication with the ends of groove 206 and opening through the radially inner surface 210 of the plate.

When a clean neutral fluid is introduced through the passages shown in FIG. 7 into the expeller cavity between the expeller plates 120' and 124', a liquid barrier is provided which effectively prevents fluid vapors or air from passing therethrough. Since the vanes on the plates 120' and 124' are pumping in opposite directions, any pressure applied from either side of this liquid barrier forces the liquid leg into the expeller vanes on the low pressure side of the arrangement thereby creating a centrifugal pressure force opposing the applied pressure to prevent the passage of vapors through the liquid barrier.

Referring now to FIG. 8 of the drawings, the invention is illustrated as incorporated in an acid pump. An impeller shaft 220 is rotatably journalled within front bearings 222 supported within a frame 224. It should be understood that the portion of the pump to the right of that illustrated is of conventional construction.

A short cylinder or pump bracket 230 is supported by the frame and has a drain outlet 232 formed through the lower part thereof. The pump bracket also includes attaching lugs 234 having holes formed therethrough for receiving bolts 236. A case plate 240 is disposed in abutting relationship to the pump bracket, and the case 242 is disposed adjacent to the case plate with a suitable gasket means 243 disposed therebetween. The case has a plurality of lugs 244 formed thereon having holes therethrough for receiving said bolts 236, nuts 246 being threaded on the outer threaded ends of the bolts for holding the components in the assembled relationship illustrated.

The case includes an inlet 250 for the liquid to be pumped. A case wear ring 252 is supported by the case adjacent the inlet. An impeller 260 of conventional construction includes a hub portion 262 threaded onto the forward threaded end of the impeller shaft 220. The primary expeller means 266 is also carried by the impeller and rotates therewith.

A case plate labyrinth ring 270 is supported within the pump bracket 230 adjacent the case plate 240. A pair of annular separator plate means 274 and 276 similar to those previously described are disposed in abutting relationship to one another and adjacent the labyrinth ring.

As in the previously described modification, a pair of auxiliary expeller plates 284 and 286 are disposed within the spaces defined by the separator plate means. These expeller plates have integral annular hub portions 288 and 290 respectively. These auxiliary expeller plates may be of any number and of any desired diameter. The expeller plates have radially extending vanes 294 and 296 formed thereon similar to the vanes of the expeller plates previously described.

A wash plate 300 is supported within the pump bracket 230, and a check valve housing 304 is connected with the wash plate by a plurality of screws 306 extending through suitable holes provided in these members.

An annular rotating seal member 310 is secured to the shaft 220, the outer periphery of this rotating seal member being spaced from the check valve housing 304 to define an outlet space 312 therebetween.

A flexible check valve diaphragm 320 formed of an annular sheet of rubber or the like is provided adjacent to the check valve housing and is held in operative position by a clamp ring 322. This diaphragm will be held in the closed position illustrated by the pressure of liquid within the pump when the pump is not operating. On the other hand, when the pump is operating, the expeller will create a vacuum moving the diaphragm to the left to eliminate rubbing contact while the pump is in operation.

A conventional front bearing cap 330 and a front hearing cap seal 332 are provided adjacent to the front bearing 222 previously described.

As in the previously described forms of the invention, close axial clearance is maintained between the vane side of each of the expeller plates and the adjacent stationary separator plate means, and a greater clearance is maintained on the side of the eXpeller plates not having vanes thereon and the adjacent stationary plate means.

The expeller plates 284 and 286 are connected for rotation with the impeller shaft 220, while the separator plate means adjacent thereto are fixed to the adjacent stationary parts of the pump. These auxiliary expeller plates serve to enhance the hydraulic seal produced when the pump is running.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the, present embodiment is therefore illustrative and not restrictive, and since the scope of the invention is defined by the appended claims, all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents are therefore intended to be embnaced by those claims.

What is claimed is:

1. A centrifugal pump having a casing, a shaft rotatable in said casing, an impeller carried by said shaft, a valvular space being defined between said shaft and said casing, valve means for opening said space when the pump is running and for closing the space at other times, and expeller means disposed between said impeller and said valve means for providing a hydraulic seal when the pump is running, said expeller means comprising a plurality of expeller means connected for rotation with said shaft and spaced from one another to enhance the hydraulic seal produced when the pump is running, said plurality of expeller means including a plurality of expeller plates spaced longitudinally along said shaft, a sleeve disposed is surrounding relationship to said shaft for holding said expeller plates in operative position, and resilient means for biasing said sleeve into operative position.

2. Apparatus as defined in claim 1 wherein said resilient means comprises an annular resilient member disposed in surrounding relationship to said shaft and engaging said sleeve.

3. A centrifugal pump having a casing, a shaft rotatable in said casing, an impeller carried by said shaft, a valvular space being defined between said shaft and said casing, valve means for opening said space when the pump is running and for closing the space at other times, and expeller means disposed between said impeller and said valve means for providing a hydraulic seal when the pump is running, said expeller means comprising a plurality of expeller means connected for rotation with said shaft and spaced from one another to enhance the hydraulic seal produced when the pump is running, said plurality of expeller means comprising a plurality of expeller plates having vanes formed thereon, separator plate means being disposed adjacent said expeller plates and therebetween, and means for introducing fluid under pressure into the space between said expeller plates and said separator plate means for purging such spaced when desired.

4. Apparatus as defined in claim 3 wherein said' means for introducing fluid under pressure is associated with the outermost portion of the separator plate means so as to introduce fluid into the space between the separator plate means and the expeller plates and to urge fluid under pressure back toward the expeller means of the pump.

5. A centrifugal pump having a casing, a shaft rotatable in said casing, tan impeller carried by said shaft, a valvular space being defined between said shaft and said casing, valve means for opening said space when the pump is running and for closing the space at other times, and expeller means disposed between said impeller and said valve means for providing a hydraulic seal when the pump is running, said expeller means comprising a plurality of expeller means connected for rotation with said shaft and spaced from one another to enhance the hydraulic seal produced when the pump is running, and means for producing a liquid barrier at an intermediate portion of said expeller means to form a vapor seal.

6. Apparatus as defined in claim 5 wherein said means for producing a liquid barrier includes a plurality of expeller plates having vanes thereon, the vanes of said expeller plates facing in opposite directions so that the expeller plates pump liquid in opposition to one another.

7. Apparatus as defined in claim 6 including means for introducing liquid under pressure to a point between said expeller plates.

8. A centrifugal pump having a casing, a shaft rotatable in said casing, an impeller carried by said shaft, a valvular space being defined between said shaft and said casing, valve means for opening said space when the pump is running and for closing the space at other times, and expeller means disposed between said impeller and said valve means for providing a hydraulic seal when the pump is running, said expeller means connected for rotation with said shaft, a sleeve disposed in surrounding relationship to said shaft for holding said expeller means in operative position axially on said shaft, and resilient means for biasing said sleeve into operative position.

References Cited UNITED STATES PATENTS 2,581,504 1/1952 Wilfley et al 103111 21,660,487 11/ 1953 Wilfley 103l11 FOREIGN PATENTS 652,168 10/ 1937 Germany. 719,353 4/ 1942 Germany. 587,372 4/ 1947 Great Britain.

HENRY F. RADUAZO, Primary Examiner US. Cl. X.R. 

